Browsing by Author "Wolkober, Marcel"

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    CAPTCHA mechanisms using semantic NLU tasks
    (2024) Wolkober, Marcel
    In 2019, one-fourth of all internet traffic was made of malicious bots. CAPTCHAs are a main countermeasure used as a test to detect non-human users. With the advancement of computational attackers using artificial intelligence, their success in these CAPTCHAs rises continuously. This bachelor’s thesis aims to provide new CAPTCHA mechanisms using semantic natural language understanding (NLU) tasks, which are generally considered hard to solve for advanced computational attackers. The task used for the NLU CAPTCHA challenges involves rating the semantic similarity of a word in two different contexts. A study with 275 participants was conducted to evaluate human usability. The study results show a high human difficulty for these challenges. Further, these challenges provide insufficient resistance against an advanced attacker. This leads to the conclusion that, in the current state, the semantic NLU CAPTCHA provides no benefit to existing CAPTCHAs. However, some challenge results indicate that with further adjustments, NLU tasks may still be relevant in use for CAPTCHA challenges.